Noise cancellation for a magnetically coupled communication link utilizing a lead frame

ABSTRACT

An integrated circuit package includes an encapsulation and a lead frame with a portion of the lead frame disposed within the encapsulation. The lead frame includes first and second conductive loops. A first voltage is induced between first and second ends of the first conductive loop in response to an external magnetic field that passes through the integrated circuit package. A second voltage is induced between third and fourth ends of the second conductive loop of the lead frame in response to the external magnetic field that passes through the integrated circuit package. The first conductive loop is coupled to the second conductive loop such that the first voltage between the first and second ends combined with the second voltage between the third and fourth ends substantially cancel.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/332,743, filed Jul. 16, 2014, now pending, which is a divisional ofU.S. patent application Ser. No. 13/677,068, filed Nov. 14, 2012, nowU.S. Pat. No. 8,818,296. U.S. patent application Ser. No. 14/332,743 andU.S. Pat. No. 8,818,296 are hereby incorporated by reference.

This application is related to U.S. patent application Ser. No.13/677,088 of Balakrishnan et al., filed Nov. 14, 2012, entitled“Magnetically Coupled Galvanically Isolated Communication Using LeadFrame,” and assigned to the Assignee of the present application.

This application is also related to U.S. patent application Ser. No.13/677,120 of Balakrishnan et al., filed Nov. 14, 2012, entitled “SwitchMode Power Converters Using Magnetically Coupled Galvanically IsolatedLead Frame Communication,” and assigned to the Assignee of the presentapplication.

BACKGROUND INFORMATION

Field of the Disclosure

The present invention relates generally to communication between atransmitter and receiver, and more specifically to communication betweena transmitter and receiver within a single integrated circuit package.

Background

Many electrical devices may rely on a communication system to sendinformation between a transmitter and a receiver to operate theelectrical device. One such communication system utilizes magneticallycoupled wires to send information between a transmitter and a receiver.Otherwise also known as inductive coupling, a current flowing throughone wire induces a voltage across the ends of another wire. The couplingbetween these wires can be strengthened in various ways. For example,the wires may be wound into coils or a magnetic core may be placedbetween the wires. Two examples of inductive coupling may be atransformer and a coupled inductor.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1A is a schematic diagram illustrating an example conceptualtransmitter receiver system, which may be used to describe the teachingsof the present invention.

FIG. 1B is a schematic diagram illustrating another example conceptualtransmitter receiver system, which may be used to describe the teachingsof the present invention.

FIG. 2A is a diagram illustrating an example of a conceptual magneticcoupling configuration with a noise cancellation loop, which may be usedto describe the teachings of the present invention.

FIG. 2B is a diagram illustrating another example of a conceptualmagnetic coupling configuration with a noise cancellation, which may beused to describe the teachings of the present invention.

FIG. 3 is a diagram illustrating an example lead frame of an integratedcircuit package in accordance with teachings of the present invention.

FIG. 4 is a diagram illustrating another example lead frame of anintegrated circuit package in accordance with teachings of the presentinvention.

FIG. 5 is a diagram illustrating yet another example lead frame of anintegrated circuit package in accordance with teachings of the presentinvention.

FIG. 6 is a diagram illustrating an example integrated circuit package,in accordance with teachings of the present invention.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings. Skilled artisans willappreciate that elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale. For example,the dimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding of variousembodiments of the present invention. Also, common but well-understoodelements that are useful or necessary in a commercially feasibleembodiment are often not depicted in order to facilitate a lessobstructed view of these various embodiments of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one having ordinary skill in the art thatthe specific detail need not be employed to practice the presentinvention. In other instances, well-known materials or methods have notbeen described in detail in order to avoid obscuring the presentinvention.

Reference throughout this specification to “one embodiment”, “anembodiment”, “one example” or “an example” means that a particularfeature, structure or characteristic described in connection with theembodiment or example is included in at least one embodiment of thepresent invention. Thus, appearances of the phrases “in one embodiment”,“in an embodiment”, “one example” or “an example” in various placesthroughout this specification are not necessarily all referring to thesame embodiment or example. Furthermore, the particular features,structures or characteristics may be combined in any suitablecombinations and/or subcombinations in one or more embodiments orexamples. Particular features, structures or characteristics may beincluded in an integrated circuit, an electronic circuit, acombinational logic circuit, or other suitable components that providethe described functionality. In addition, it is appreciated that thefigures provided herewith are for explanation purposes to personsordinarily skilled in the art and that the drawings are not necessarilydrawn to scale.

As mentioned above, electrical devices may utilize magneticcommunication between a transmitter and a receiver to operate. Oneexample device may be a synchronous flyback converter. The synchronousflyback converter is an example power converter topology which utilizestwo active switches to control the transfer of energy from an input toan output of the power converter. Power converters are commonly used dueto their high efficiency, small size, and low weight to power many oftoday's electronics. One active switch (referred to as a primary switch)is coupled to the primary winding (also referred to as the inputwinding) of an energy transfer element while the other active switch(referred to as a secondary switch) is coupled to the secondary winding(also referred to as the output winding) of the energy transfer element.In general, a controller controls each active switch. For instance, theprimary switch is generally controlled by a primary controller and thesecondary switch is generally controlled by a secondary controller. Thesecondary controller may be one example of a transmitter while theprimary controller may be one example of a receiver.

The primary and secondary controllers are utilized to regulate theoutput of the power converter by sensing and controlling the output ofthe power converter in a closed loop. More specifically, either theprimary or the secondary controller (or both) may be coupled to a sensorthat provides feedback information about the output of the powerconverter in order to regulate the output quantity that is delivered tothe load. The output of the power converter is regulated by controllingthe turn on and turn off of the primary and secondary switches inresponse to the feedback information.

Further, the primary and secondary switches cannot be on at the sametime in a synchronous flyback converter. In general, an open switch isconsidered to be off and does not normally conduct current. A closedswitch is generally considered to be on and may conduct current. Thus,the primary and secondary controllers of a synchronous flyback converterare synchronized to ensure the primary and secondary switches do notconduct current simultaneously. In other words, the primary andsecondary controllers communicate to regulate the output of the powerconverter and to ensure that the primary and secondary switches are noton at the same time.

In general, the primary and secondary controllers are implemented asintegrated circuits (ICs), which are in their own separate integratedcircuit packages. External circuits are often used to facilitatecommunication between the primary and secondary controllers while at thesame time provide the necessary galvanic isolation in order to complywith the safety requirements.

An integrated circuit package typically includes a lead frame. The leadframe provides mechanical support for the die or dice that may be withinthe integrated circuit package. In general, the lead frame typicallyincludes a die attach pad to which a semiconductor die may be attached.In addition, the lead frame generally also includes leads that serve aselectrical connections to circuits external from the integrated circuitpackage. The lead frame is generally constructed from a flat sheet ofmetal. The flat sheet of metal may be stamped, etched, punched, etc.,with a pattern, which defines the die attach pads and various leads ofthe lead frame. For the purposes of this disclosure, the term“integrated circuit package” refers to the type of packages usedgenerally for integrated circuits. Some embodiments of this inventionmay have no integrated circuits in the package.

Examples in accordance with the teachings of the present inventionutilize the lead frame to provide a magnetically coupled galvanicallyisolated communication link between a transmitter and receiver as wellas provide noise cancellation. In some embodiments, the transmitter andreceiver may be within the same integrated circuit package. Embodimentsof the invention utilize the lead frame to facilitate communicationbetween the transmitter and receiver using transmitter and receiverloops formed in the lead frame. Further, embodiments of the presentinvention utilize a cancellation loop formed in the lead frame which mayimprove the susceptibility to magnetic fields external from theintegrated circuit package. These external magnetic fields may also bereferred to as noise.

As will be discussed, galvanically isolated conductors are defined inthe lead frame, and magnetically coupled conductive loops are definedwith the isolated conductors in accordance with the teachings of thepresent invention. In various examples, the conductive loops included inthe conductors of the lead frame may serve as transmit loops, receiveloops, and/or cancellation loops. In one example, the receive loop andcancellation loop are substantially the same size and shape and arewound in opposite directions. In an example the receive loop and thetransmit loop are magnetically coupled to each other. In addition, thereceive loop may be surrounded by the transmit loop. In another example,the receive loop may surround the transmit loop. In one example, thereceive loop, the transmit loop and the cancellation loop in the leadframe each consist of one turn. In general, a wrap of wire or otherconductive material forming a loop may be considered a turn. Severalwraps of wire or other conductive material may be considered multipleturns. Current in an electrical circuit should travel in a closed path.For the purpose of this application, a physical closed path for currentmay be referred to as a loop. A loop may include different elements suchas conductors (that in examples of this disclosure could be formed bylead frame and bond wires inside an integrated circuit package) as wellas electrical components that are in path of the circulating current.Each element of the loop forms a part of the loop and a combination ofone or more elements in the loop is referred to as a partial loop. Inthe context of magnetic field coupling, a loop enclosing a magneticfield is typically referred to as having one or more turns. Each turncorresponds to one enclosure of the magnetic field.

The lead frame is generally already a part of integrated circuitpackaging. However, by utilizing conductive loops defined bygalvanically isolated conductors included in the lead frame itself toprovide a magnetically coupled communication link between thetransmitter and receiver and provide noise cancellation in accordancewith the teachings of the present invention, very little cost is added.Utilizing the lead frame may also reduce the overall size of the powersupply. In addition, utilizing the lead frame may also reduce theoverall cost of the package.

It is noted that an example isolated synchronous switch mode flybackpower converter, in which the secondary controller includes atransmitter circuit and the primary controller includes a receivercircuit is described in the present disclosure for explanation purposes.It is appreciated, however, that other example topologies of switch modepower converters and/or other circuits in general may also benefit froman integrated circuit package including a magnetically coupledcommunication link defined by galvanically isolated conductive loopsincluded in the lead frame to communicate between the transmitter andreceiver and provide noise cancellation in accordance with the teachingsof the present invention. Further, while examples in accordance with theteachings of the present invention are discussed in connection withcommunication between a transmitter and a receiver for explanationpurposes, it is appreciated that systems utilizing transceivers may alsobenefit from the teachings of the present invention.

Referring first to FIG. 1A, a schematic diagram illustrating aconceptual system 100 is shown including a cancellation winding 112 inaccordance with the teachings of the present invention. It isappreciated that the conceptual system 100 shown in FIG. 1A is utilizedto explain teachings of the present invention. As illustrated in FIG.1A, system 100 includes a magnetic coupling element 104 that has atransmitter winding 108, a receiver winding 110 and a cancellationwinding 112. In the illustrated example, one end of receiver winding 110is coupled to one end of cancellation winding 112 as shown. Atransmitter 102 is coupled to transmitter winding 108 and a receiver 106is coupled to receiver winding 110 and cancellation winding 112 asshown. Further shown in FIG. 1A, transmitter winding 108 conducts atransmitter current I_(T) 116 and there is a transmitter voltage V_(T)114 across transmitter winding 108. Receiver winding 110 andcancellation winding 112 conduct a receiver current I_(R) 120 and thereis a receiver voltage V_(R) 118 across receiver winding 110 andcancellation winding 112 as shown. In addition, FIG. 1A illustrates anoise block 111 and a noise winding 113. It should be appreciatedhowever, that the noise block 111 and noise winding 113 are illustrativeand are included in FIG. 1A to model the effects of noise on the system100 for explanation purposes rather than representing a physical noisegenerating circuit block 111 coupled to a winding 113 wound on magneticcoupling element 104.

It is also noted that the dots and triangles shown in FIG. 1A representthe direction of current and polarity of voltage that one windinginduces in another due to the magnetic coupling between the windings. Inparticular, the dot denotes the direction of current and the polarity ofvoltage induced in the receiver winding 110 and cancellation winding 112due to the magnetic coupling from the transmitter winding 108. Thetriangle denotes the direction of current and polarity of voltageinduced in the receiver winding 110 and cancellation winding 112 due tothe magnetic coupling from noise winding 113. In other words, the dotsand triangles help to illustrate the relationship of the windings withrespect to each other, which will also be discussed in further detailbelow with respect to FIGS. 2A and 2B.

Transmitter 102 is coupled to the transmitter winding 108 of magneticcoupling element T1 104 such that the transmitter current I_(T) 116flows into the transmitter winding 108, as indicated by the dot shown inFIG. 1A. In addition, the voltage drop across the transmitter winding108 is indicated by the dot and is denoted as transmitter voltage V_(T)114. Magnetic coupling element T1 104 also includes a receiver winding110 and cancellation winding 112. One end of the receiver winding 110,which is the end indicated by both the dot and the triangle in FIG. 1A,is coupled to the receiver 106, while the end of the cancellationwinding 112 indicated by the triangle is further coupled to the receiver106 as shown in FIG. 1A. The end of the receiver winding without the dotand triangle is coupled to the end of the cancellation winding 112indicated by the dot as shown in FIG. 1A. The voltage received byreceiver 106 is denoted as receiver voltage V_(R) 118, and thecorresponding current is denoted as receiver current I_(R) 120. Thetransmitter 102 may send information to the receiver 106 through themagnetic coupling between the transmitter winding 108, receiver winding110, and cancellation winding 112. The transmitter 102 may communicateinformation as a voltage signal and/or a current signal and the receiver106 may receive the information as a voltage signal and/or currentsignal. In embodiments, the transmitter 102 may communicate informationutilizing the transmitter current I_(T) 116. In one example, circuitswithin transmitter 102 may control various properties of the transmittercurrent I_(T) 116 to communicate information to the receiver 106. Whenthe transmitter current I_(T) 116 is changing in magnitude, it producesa changing magnetic field in the proximity of a conductor. Inembodiments, both the receiver winding 110 and cancellation winding 112are conductors. Due to the laws of electromagnetic induction, a voltageis generated across a conductor that is subjected to a changing magneticfield. In embodiments therefore, receiver voltage V_(R) 118 is induceddue to the changing magnetic field generated by changes in transmittercurrent I_(T) 116 and may result in receiver current I_(R) 120. Thereceiver 206 includes circuits which may receive the transmitter inducedvoltage and/or current and interpret the voltage and/or current asinformation. Properties of the transmitter current I_(T) 116 which maybe controlled to communicate information may include the magnitude andthe rate of change of the transmitter current I_(T) 116. Thecommunicated signals may take the form of digital information or ofanalog information. In the case of digital information, communicationcan be in the form of binary signals or more complex encoded digitaldata as will be known to one skilled in the art. It should beappreciated that other communication techniques may be used. In otherexamples, communication techniques which take advantage of therelationship between the transmitter current I_(T) 116 and the resultantinduced receiver voltage V_(R) 118 and receiver current I_(R) 120received by the receiver 106 may be utilized.

Further illustrated in FIG. 1A is a noise block 111 and a noise winding113. It is appreciated that block 111 and noise winding 113 are shown indashed lines in FIG. 1A for the purpose of modeling the effects of noiseon the system 100. In particular, noise that is external to the system100 may impact the transmission of information between the transmitter102 and receiver 106. For example, noise block 111 may correlate toother electronics or systems that produce unwanted electromagneticinterference (EMI). Thus, noise winding 113 correlates to the effectsthat noise block 111 has on system 100. In other words, noise block 111and noise winding 113 may be utilized to model the effects of externalmagnetic fields on the system 100.

As shown in FIG. 1A, the current I_(T) 116 in the transmitter winding116 may induce a current and voltage in the receiver winding 110 asindicated by the dot. The induced current flows out from the end of thereceiver winding 110 indicated by the dot. There is a voltage drop fromthe end of the receiver winding 110 indicated by the dot to the otherend of receiver winding 110. Transmitter current I_(T) 116 also inducesa current and voltage in the cancellation winding 112 as indicated bythe dot. The induced current flows out from the end of the cancellationwinding 112 indicated with a dot. There is a voltage drop from the endof the cancellation winding 112 indicated by the dot to the other end ofcancellation winding 112.

The cancellation winding 112 is magnetically coupled out of phase withthe transmitter winding 108. As shown in FIG. 1A, the position of thedot for the cancellation winding 112 is in the opposite location fromthe position of the dot for the transmitter winding for the respectivewindings. The transmitter winding 114 is however, magnetically coupledin phase with the receiver winding 110. The position of the dot for boththe transmitter winding 114 and the receiver winding 110 is in the samecorresponding location for the respective windings. Further, thecancellation winding 112 and the receiver winding 110 are magneticallycoupled out of phase with each other. As shown, the cancellation winding112 and the receiver winding 110 create a “figure eight” shape in theillustrated example. Stated in another way, the cancellation winding 112and the receiver winding 110 are wound in opposite directions withrespect to each other. For instance the cancellation winding 112 may bewound in a clockwise direction and the receiver winding would then bewound in a counter-clockwise direction.

In various examples, the coupling of one end of the receiver winding 110to one end of the cancellation winding 112 as shown may strengthenreceived signals from the transmitter 102, as will be further discussedbelow with respect to FIG. 2B. The transmitter current I_(T) 116 inducesa current and voltage for both receiver winding 110 and the cancellationwinding 112. Receiver current I_(R) 120 is the current that flowsthrough both the receiver winding 110 and cancellation winding 112. Inaddition, the transmitter 102 induced receiver voltage V_(R) 118 is thecombination or sum of the voltages across receiver winding 110 andcancellation winding 112.

Noise, such as for example external magnetic fields, which is modeled asnoise block 111 and noise winding 113, may also induce a voltage in thereceiver winding 110 and cancellation winding 112. The voltage drop inthe receiver winding 110 is from the end of the receiver winding 110indicated by the triangle to the other end of receiver winding 110. Inaddition, the voltage drop in the cancellation winding 112 due to noiseis from the end of the cancellation winding 112 indicated by thetriangle to the other end of cancellation winding 112.

Both the receiver winding 110 and the cancellation winding 112 aremagnetically coupled in phase with the noise winding 113. As illustratedin FIG. 1A, the position of the triangle is in the same correspondinglocation for the noise winding 113, receiver winding 110, andcancellation winding 112. However, as mentioned above, the receiverwinding 110 and the cancellation winding 112 are magnetically coupledout of phase to each other. The noise induced receiver voltage V_(R) 118is the difference between the voltage across the receiver winding 110and the cancellation winding 112. If the receiver winding 110 andcancellation winding 112 are substantially similar in size and number ofturns, there is substantially no receiver current I_(R) 120 due to noiseand the receiver voltage V_(R) 118 due to noise is substantially zero.In other words, in the illustrated example, as the receiver winding 110and cancellation winding 112 are substantially similar in size andnumber of turns, the noise signal component induced in the receiverwinding 110 in response to the noise winding 113 is substantially equaland opposite to the noise signal component induced in the cancellationwinding 112 in response to the noise winding 113. As such, the noisesignal components induced in each respective receiver winding 110 andcancellation winding 112 substantially cancel out each other.

For communication between a transmitter and receiver within anintegrated circuit package, the transmitter winding 108, receiverwinding 110, and cancellation winding 112 may be implemented usingmagnetically coupled galvanically isolated conductive loops defined inthe lead frame of the integrated circuit package in accordance with theteachings of the present invention, as will be further discussed belowwith respect to FIGS. 3,4, and 5.

FIG. 1B illustrates a schematic of another conceptual system 101including transmitter 102, magnetic coupling element 104, receiver 106,transmitter winding 108, receiver winding 110, cancellation winding 112,and an arithmetic operator 122. Further shown in FIG. 1B is transmittervoltage V_(T) 114 and transmitter current I_(T) 116. In addition, FIG.1B illustrates noise block 111 and noise winding 113. It is appreciatedthat the conceptual system 101 shown in FIG. 1B is utilized to explainteachings of the present invention.

It is appreciated that system 101 shown in FIG. 1B shares manysimilarities with the system 100 shown in FIG. 1A. However, onedifference is that instead of being coupled together as shown in FIG.1A, the receiver winding 110 and the cancellation winding 112 areseparately coupled to an arithmetic operator 122 in FIG. 1B. Inparticular, as shown in FIG. 1B, both ends of the receiver winding 110and both ends of the cancellation winding 112 are each separatelycoupled to arithmetic operator 122. As mentioned above, the transmitter102 induces a current and voltage in both the receiver winding 110 andthe cancellation winding 112. Noise from noise block 111 may also affectthe induced current and voltages of the receiver winding 110 and thecancellation winding 112. In the illustrated example, the arithmeticoperator 122 may receive the induced voltages and currents of thereceiver winding 110 and the cancellation winding 112 as input signals.

In addition, in the example one end of the receiver winding 110 and oneend of the cancellation winding 112 are coupled to ground 121. Asillustrated, the end of the receiver winding 110 without the dot andtriangle is coupled to ground 121. For the cancellation winding 112, theend of the winding denoted by the dot is coupled to ground 121.

In one example, the arithmetic operator 122 includes a circuit that mayperform a number of arithmetic operations such as addition, subtraction,multiplication and division to the various inputs to the arithmeticoperator 122 to provide a resultant output. In various examples, thevarious inputs and outputs of the arithmetic operator 122 may includecurrent signals, voltage signals or both. In one example, the arithmeticoperator 122 may perform subtraction. For the example shown in FIG. 1B,both the receiver winding 110 and the cancellation winding 112 aremagnetically coupled in phase with the noise winding 113. As such, thearithmetic operator 122 would subtract the magnitude of the voltage orcurrent of the cancellation winding 112 from the magnitude of thevoltage or current of the receiver winding 110 and result insubstantially zero voltage or current. In other words, the receiver 122may subtract the magnitude of the signal provided by the receiverwinding 110 from the magnitude of the signal provided by thecancellation winding.

In the illustrated example, the receiver winding 110 is coupled in phasewith the transmitter winding 108 while the cancellation winding 112 iscoupled out of phase with the transmitter winding 108. In oneembodiment, the arithmetic operator 122 is a subtractor. However, sincethe transmitter winding 108 and the cancellation winding 112 are coupledout of phase, the signal induced in cancellation winding 112 due to atransmit signal in winding 108 would provide to the arithmetic operator122 a signal of opposite polarity. The resultant arithmetic operation iseffectively addition thus acting to supplement the receive signal fromwinding 110. Thus, magnetically coupled signals induced in receiverwinding 110 and the cancellation winding 112 due to a changing magneticfield generated by current flow in the transmitter winding 108 areadditive. As such, the information sent by the transmitter 102 isstrengthened.

For communication between a transmitter and receiver within anintegrated circuit package, the transmitter winding 108, receiverwinding 110, and cancellation winding 112 may be implemented usingmagnetically coupled galvanically isolated conductive loops defined inthe lead frame of the integrated circuit package in accordance with theteachings of the present invention, as will be further discussed belowwith respect to FIGS. 3 and 4.

FIG. 2A illustrates an example conceptual magnetic couplingconfiguration of a system 200 with a cancellation loop 212. It isappreciated that the conceptual system 200 shown in FIG. 2A is utilizedto explain teachings of the present invention. System 200 includes areceiver 206, a receiver loop 210 (which is one example of receiverwinding 110), a cancellation loop 212 (which is one example ofcancellation winding 112), nodes 232, 234, 236, 238, 240, and 242, andmarker 258. Further shown in FIG. 2A is a receiver voltage V_(R) 218, areceiver current I_(R) 220, a voltage V_(RN) 266, and a voltage V_(CN)268. In addition, FIG. 2A illustrates noise block 211 and noise loop 213(which is one example of noise winding 113). It should be appreciatedhowever, that noise block 211 and noise winding 213 are included in FIG.2A to model the effects of noise on the system 200. FIG. 2A is oneexample of a magnetic coupling configuration of the receiver winding andcancellation winding illustrated in FIG. 1A. The transmitter andtransmitter winding are not shown in FIG. 2A, but will be discussedbelow with respect to FIG. 2B.

As illustrated, receiver loop 210 includes nodes 236 and 238 locatedproximate to the ends of receiver loop 210 while cancellation loop 212includes nodes 240 and 242 located proximate to the ends of cancellationloop 212 and receiver 206 includes nodes 232 and 234. Receiver loop 210and cancellation loop 212 are coupled to receiver 206 such that node 232of the receiver 206 is coupled to node 236 of receiver loop 210, node234 of the receiver 206 is coupled to node 240 of cancellation loop 212,and node 238 of the receiver loop 210 is coupled to node 242 of thecancellation loop 212. In the example illustrated in FIG. 2A thereceiver loop 210 and the cancellation loop 212 are illustrated assubstantially similar squares and are wound in opposite directions asshown. As in other various examples, the receiver loop 210 andcancellation loop 212 may be substantially the same size and shape. Inone embodiment, the areas substantially surrounded by the receiver loop210 and the cancellation loop 212 are substantially the same size.However, it should be appreciated that the receiver loop 210 andcancellation loop 212 may be different sizes and/or shapes. Further, insome embodiments, the areas substantially surrounded by the receiverloop 210 and the cancellation loop 212 may be different.

Further, the voltage drop between nodes 232 and 234 is denoted asreceiver voltage V_(R) 218. The voltage drop between nodes 236 and 238is denoted as voltage V_(RN) 266 and the voltage drop between nodes 240and 242 is denoted as voltage V_(CN) 268. Receiver current I_(R) 220 isillustrated as current flowing from node 232 to receiver 206.

In addition, FIG. 2A illustrates noise block 211 and noise winding 213,which is used to model the effects of noise, such as external magneticfields, to the system 200 on both the receiver winding 210 andcancellation winding 212. As illustrated, the noise winding 213substantially surrounds the receiver winding 210 and cancellationwinding 212. Triangles shown in FIG. 2A denote the polarity of thereceiver loop 210 and cancellation loop 212 with respect to the noiseloop 213.

In FIG. 2A, noise is modeled as noise block 211 and current flowing innoise loop 213. For the example shown, current in the noise loop 213 isflowing in a clockwise direction and generates a magnetic field thatpasses through planes of both the receiver loop 210 and the cancellationloop 212. Markers 258 illustrate the overall magnetic field that passesthrough both receiver loop 210 and cancellation loop 212. In general,the “X” symbol as illustrated for markers 258 denotes magnetic field orflux into the page, while a dot symbol for a marker symbol denotesmagnetic field or flux out from the page. Due to the positioning of thereceiver loop 210 and cancellation loop 212 with respect to the noiseloop 213, the overall effects of the magnetic field on both receiverloop 210 and the cancellation loop 212 are substantially similar as themagnetic field or flux from the noise loop passes through the planes ofboth receiver loop 210 and the cancellation loop 212 in substantiallythe same direction into the page, as illustrated in the example of FIG.2A with markers 258.

The change in magnetic fields that passes through the planes of thereceiver loop 210 and cancellation loop 212 induces an electric fieldfor both loops. For the example shown in FIG. 2A, the direction of theelectric field for receiver loop 210 and cancellation loop 212 is in acounter clockwise direction for increasing magnetic field strength inthe direction shown by marker 258. In other words, the increasingmagnetic field due to noise winding 213 induces a voltage drop acrossnodes 236 and 238, denoted as voltage V_(RN) 266, which is the voltageof the receiver loop 210 due to noise. The changing magnetic field dueto the noise also induces a voltage drop across nodes 240 and 242,denoted as voltage V_(CN) 268, which is the voltage of the cancellationloop 212 due to noise. Triangles shown in FIG. 2A denote the polarity ofthe receiver loop 210 and cancellation loop 212 with respect to thenoise loop 213.

In various examples, due to the coupling of the receiver loop 210 andthe cancellation loop 212, the receiver voltage V_(R) 218 is determinedaccording to equation (1):V _(R) =V _(RN) −V _(CN)  (1)Thus, the receiver voltage V_(R) 218 received by receiver 206 is thedifference between the voltage V_(RN) 266 and the voltage V_(CN) 268.Both the receiver loop 210 and the cancellation loop 212 are coupled inphase with the noise loop 213. However, both receiver loop 210 and thecancellation loop 212 are coupled out of phase with each other. Indeed,in the illustrated example, receiver loop 210 is wound in an oppositedirection from cancellation loop 212. Thus, if the receiver loop 210 andcancellation loop 212 are substantially the same size and shape and themagnetic fields that pass through the planes of both loops aresubstantially the same, then the magnitudes of voltages V_(RN) 266 andV_(CN) 268 are substantially the same. The receiver 206 would receivesubstantially no voltage due to noise. Further, the receiver 206 wouldreceive no current due to noise. As such, the effects of noise to thereceiver 206 may be substantially minimized. In addition, it should beappreciated that the effects of noise are still cancelled if thedirection of the magnetic field due to noise is out of the page. Forthat case, markers 258 would be the dot symbols instead of the “X”symbols, and the receiver voltage V_(R) 218 is still the differencebetween the magnitudes of voltage V_(RN) 266 and voltage V_(CN) 268.

For communication between a transmitter and a receiver within anintegrated circuit package, the transmitter winding 108, receiverwinding 110, and cancellation winding 112 may be implemented usingmagnetically coupled galvanically isolated conductive loops defined inthe lead frame of the integrated circuit package in accordance with theteachings of the present invention, as will be further discussed withrespect to FIGS. 3, 4, and 5. Examples of the present invention includea transmitter and receiver within the same integrated circuit packagewhich utilize conductive loops formed in the lead frame to communicate.Magnetic fields produced outside the integrated circuit package may beconsidered external magnetic fields while magnetic fields produced bycomponents within the integrated circuit package may be consideredinternal magnetic fields. The magnetic field produced by the current inthe noise loop 213 may model an external magnetic field which mayinterfere with communication between the transmitter and receiver.Embodiments of the present invention utilize the cancellation loop 212to reduce the effects which external magnetic fields may have oncommunications between the transmitter and receiver.

FIG. 2B illustrates an example conceptual magnetic couplingconfiguration of a system 200 with a cancellation loop 212. It isappreciated that the conceptual system 200 shown in FIG. 2B is utilizedto explain teachings of the present invention. System 200 includes atransmitter 202, receiver 206, a transmitter loop 208 (which is oneexample of transmitter winding 108), receiver loop 210, cancellationloop 212, nodes 224, 226, 228, 230, 232, 234, 236, 238, 240, and 242,and markers 244 and 248. Further shown in FIG. 2B is transmitter voltageV_(T) 214, transmitter current I_(T) 216, receiver voltage V_(R) 218,receiver current I_(R) 220, a voltage V_(R) T 252, a voltage V_(CT) 254.FIG. 2B illustrates one example of a magnetic coupling configuration ofthe receiver winding and cancellation winding illustrated in FIG. 1A.

The receiver 206, receiver loop 210 and cancellation loop 212, arecoupled as described above with respect to FIG. 2A. Further shown istransmitter 202 and transmitter loop 208. Transmitter 202 includes nodes224 and 226 while transmitter loop 208 includes nodes 228 and 230. Nodes224 and 226 of the transmitter 202 are coupled to nodes 228 and 230 ofthe transmitter loop 208, respectively. As illustrated, the receiverloop 210 is substantially surrounded by the transmitter loop 208.Further, the voltage drop across node 224 and 226 (or in other words,across node 228 and 230) is denoted as transmitter voltage V_(T) 214.FIG. 2B also shows transmitter current I_(T) 216, which is shown asflowing from node 224 to node 226 through the transmitter loop 208.

For the example shown in FIG. 2B, transmitter current I_(T) 216 in thetransmitter loop 208 flows in a clockwise direction and generates amagnetic field which passes through both the receiver loop 210 and thecancellation loop 212. Markers 244 and 248 illustrate the overallmagnetic field seen by both receiver loop 210 and cancellation loop 212due to the current in transmitter loop 208. Due to the positioning ofthe receiver loop 210 and cancellation loop 212 with respect to thetransmitter loop 208, the receiver loop 244 experiences an overallmagnetic field as going into the page, as illustrated with the “X”symbol for maker 244, while the cancellation loop 212 experiences anoverall magnetic field out of the page, as illustrated with the dotsymbol for marker 248. When the transmitter 202 and receiver 206 arewithin the same integrated circuit package, the magnetic field producedby the transmitter current I_(T) 216 may be considered an internalmagnetic field.

The change in magnetic fields experienced by the receiver loop 210 andcancellation loop 212 induces an electric field for both loops. For theexample shown, the direction of the electric field for the receiver loop210 is in the counter clockwise direction while the direction of theelectric field for the cancellation loop 212 is in the clockwisedirection for increasing magnetic field strength in the directions shownby markers 244 and 248. In other words, the changing magnetic field dueto transmitter loop 208 induces a voltage drop across the ends ofreceiver loop 210 at nodes 236 and 238, denoted as voltage V_(RT) 252,which is the voltage of the receiver loop 210 due to the transmitter202. The changing magnetic field also induces a voltage drop across theends of cancellation loop 212 at nodes 242 and 240, denoted as voltageV_(CT) 254, which is the voltage of the cancellation loop 212 due to thetransmitter 202. Dots shown in FIG. 2B denote the polarity of thereceiver loop 210 and cancellation loop 212 with respect to thetransmitter loop 208.

As discussed above, the transmitter 202 may communicate informationutilizing the transmitter current I_(T) 216. Circuits within transmitter202 may control various properties of the transmitter current I_(T) 216to communicate information to the receiver 206. When the transmittercurrent I_(T) 216 is changing in magnitude, it produces a changingmagnetic field which induces a voltage across the receiver winding 210and cancellation winding 212 due to the laws of electromagneticinduction. In embodiments, receiver voltage V_(R) 218 is induced due tothe changing magnetic field generated by changes in transmitter currentI_(T) 216 and may result in receiver current I_(R) 220. Circuitsincluded in the receiver 206 may receive the transmitter induced voltageand/or current and interpret the voltage and/or current as information.Properties of the transmitter current I_(T) 216 which may be controlledto communicate information may include the magnitude and the rate ofchange of the transmitter current I_(T) 216. The communicated signalsmay take the form of digital information or of analog information. Inthe case of digital information, communication can be in the form ofbinary signals or more complex encoded digital data as will be known toone skilled in the art. It should be appreciated that othercommunication techniques may be used. In other examples, communicationtechniques which take advantage of the relationship between thetransmitter current I_(T) 216 and the resultant induced receiver voltageV_(R) 218 and receiver current I_(R) 220 received by the receiver 206may be utilized.

In one example, the transmitter 202 may include a controlled currentsource which produces the transmitter current I_(T) 216. The controlledcurrent source may vary properties of the transmitter current I_(T) 216to communicate information to the receiver 206. Further, the receiver206 may include a comparator which compares the receiver voltage V_(R)218 with a reference voltage V_(TH). The receiver 206 may utilize theoutput of the comparator to interpret the information communicated bythe transmitter 202. For the example of a flyback converter in which thesecondary controller may be a transmitter and the primary controller maybe a receiver circuit and, the secondary controller may communicateinformation to the primary controller to turn on or off the primaryswitch to regulate the output of the power converter. The secondarycontroller (transmitter) may produce the transmitter current I_(T)(utilizing a controlled current source) when the primary switch shouldbe turned on. When the primary controller (receiver) receives an inducedreceiver voltage V_(R), which is greater than a reference voltageV_(TH), the primary controller processes the information to determinewhether to turn on the primary switch. In one example, the absence ofthe transmitter current I_(T) (and hence receiver voltage V_(R)) couldindicate to the primary controller (receiver) to not turn on the primaryswitch.

The receiver loop 210 is magnetically coupled in phase with thetransmitter loop 208 while the cancellation loop 212 is magneticallycoupled out of phase with the transmitter loop 208. In addition, thecancellation loop 212 and the receiver loop 210 are magnetically coupledout of phase to each other. In various examples, due to the magneticcoupling of the receiver loop 210 and the cancellation loop 212, thereceiver voltage V_(R) 218 is determined according to equation (2):V _(R) =V _(RT) +V _(CT)  (2)Thus, the receiver voltage receiver voltage V_(R) 218 is the sum of thevoltage V_(RT) 252 and the voltage V_(CT) 254. As such, the informationsent by transmitter 202 may be strengthened with the addition ofcancellation loop 212 in accordance with the teachings of the presentinvention. Thus, it is appreciated that magnetically coupled signalsinduced in receiver winding 210 and the cancellation winding 212 due toa changing magnetic field generated by current flow in the transmitterwinding 208 are additive.

For communication between a transmitter and receiver within anintegrated circuit package, the transmitter winding 108, receiverwinding 110, and cancellation winding 112 may be implemented usingmagnetically coupled galvanically isolated conductive loops defined inthe lead frame of the integrated circuit package in accordance with theteachings of the present invention, as will be further discussed withrespect to FIGS. 3, 4, and 5.

To illustrate, FIG. 3 shows an example lead frame 300 disposedsubstantially within an encapsulated portion of an integrated circuitpackage in accordance with the teachings of the present invention. Inthe illustrated example, lead frame 300 includes a first conductorincluding a receiver conductive loop 310 (which is one example ofreceiver loop 210) and a cancellation conductive loop 312 (which is oneexample of cancellation loop 212). As shown in the illustrated example,lead frame 300 also includes a second conductor that is galvanicallyisolated from the first conductor. In the illustrated example, thesecond conductor includes transmitter conductive loop 308 (which is oneexample of transmitter loop 208). As shown in the illustrated example,the transmitter conductive loop 308 is disposed proximate to thereceiver conductive loop 310 to provide a magnetically coupledcommunication link between the transmitter conductive loop 308 and thereceiver conductive loop 310 in accordance with the teachings of thepresent invention. In addition, FIG. 3 also shows leads 372 and 374, adie attach pad 376, and a die attach pad 378. The square numbered as 371illustrates the encapsulated portion of the lead frame 300. In otherwords, elements within the encapsulation 371 are disposed within theencapsulated portion of the integrated circuit package. Further shown inFIG. 3 is a transmitter 302, a receiver 306, pads 379, 380, 381, and382, and bond wires 383. 384, 385 and 386. FIG. 3 is one example of amagnetic coupling configuration of a transmitter winding, receiverwinding, and cancellation winding as discussed with respect to the FIGS.1A, 2A, and 2B.

In one example, transmitter 302 and receiver 306 are implemented ascircuits in integrated circuit dice included within the encapsulatedportion of the integrated circuit package. The die attach pad 376, whichis part of the second conductor of lead frame 300, is denoted bydiagonal cross-hatching in FIG. 3 and denotes the portion of the leadframe 300 onto which transmitter 302 is mounted. Similarly, the dieattach pad 378, which is part of the first conductor of lead frame 300,is shaded with diagonal cross-hatching in FIG. 3 and denotes the portionof the lead frame 300 onto which the receiver 306 is mounted. In oneexample, the receiver 306 and transmitter 302 are attached to therespective isolated first and second conductors of the lead frame 300utilizing an adhesive. The adhesive may be non-conductive. In anotherexample, the adhesive may be conductive. In one example, the slot in dieattach pad 376 shown under the transmitter 302 may make the transmitterconductive loop 308 longer. As such, the current through the transmitterconductive loop 308 may flow closer and parallel to the receiverconductive loop 310 to improve magnetic coupling.

Leads 372 and 374 denote portions of the lead frame 300 which may coupleto circuits that are external to the integrated circuit package (inother words, outside of profile 371). Although not shown, various bondwires may couple either the transmitter 302 or the receiver 306 to anyof the leads 372 or 374.

The portion of the lead frame 300 shaded by densely packed dots in FIG.3 corresponds to the transmitter conductive loop 308. The portion oflead frame 308 and bond wires 383 and 384 complete the transmitterconductive loop. In one example, bond wire 384 is attached to theportion of lead frame 300 corresponding to the transmitter conductiveloop 308 utilizing known bonding techniques. Further, the bond wire 384is coupled to transmitter 302 through pad 380. Bond wire 383 is attachedto the portion of the die attach pad 376 corresponding to thetransmitter conductive loop 308 utilizing known bonding techniques.Further the bond wire 383 is coupled to the transmitter 302 through pad381. In one example, bondwire 383 and pad 381 provide the coupling toground for the transmitter conductive loop 308.

The portion of the lead frame 300 shaded by dots in FIG. 3 correspondsto the receiver conductive loop 310. Further portion of the lead frame300 shaded by cross-hatching in FIG. 3 corresponds to the cancellationconductive loop 312. The portion of the lead frame corresponding to boththe receiver conductive loop and the cancellation conductive loop may beconsidered a first conductor while the portion of the lead framecorresponding to the transmitter conductive loop 308 may be considered asecond conductor. Bond wire 386 is attached to the portion of lead frame300 corresponding to cancellation conductive loop 312 utilizing knownbonding techniques. Bond wire 386 couples the cancellation conductiveloop 312 to the receiver 306 through pad 382 to complete the receiverconductive loop 310 and cancellation conductive loop 312. Further, bondwire 385 is attached to die attach pad 378 using known bondingtechniques and is coupled to the receiver 306 through pad 379. In oneexample, bond wire 385 and pad 379 provide the coupling to ground forthe receiver conductive loop 310 and the cancellation conductive loop312. As shown in the example depicted in FIG. 3, beginning from areference point such as for example pad 379, receiver conductive loop310 is wound in a counter-clockwise direction while cancellationconductive loop 312 is wound in an opposite or clockwise directionrelative to receiver conductive loop 310. As illustrated, thetransmitter conductive loop 308 substantially surrounds the receiverconductive loop 310 and the receiver conductive loop 310 is magneticallycoupled out of phase with the cancellation conductive loop 312. In theillustrated example, transmitter conductive loop 308 is wound in theclockwise direction from a reference point such as pad 380 oftransmitter 302. In general, the transmit signal is sent from the pad380 in a clockwise direction around transmitter conductive loop 308. Inone example, the transmitter conductive loop 308 substantially surroundsthe receiver conductive loop 310. In one example, the transmitterconductive loop 308, the receiver conductive loop 310, and thecancellation conductive loop 312 are all encapsulated in insulatingmaterial within the encapsulated portion of the integrated circuitpackage and are all disposed substantially in the same plane.

By utilizing galvanically isolated magnetically coupled conductive loopsof the lead frame to provide a communications link between thetransmitter and receiver with noise cancellation, very little cost isadded. In addition, utilizing the lead frame may also reduce the overallsize of the power converter and the cost of the package in accordancewith the teachings of the present invention.

FIG. 4 illustrates another example of a lead frame 400 disposedsubstantially within the encapsulated portion of an integrated circuitpackage in accordance with the teachings of the present invention. Inthe illustrated example, lead frame 400 includes a first conductorincluding receiver conductive loop 410 (which is one example of receiverloop 110) and a cancellation conductive loop 412 (which is one exampleof cancellation winding 112). As shown in the illustrated example, leadframe 400 also includes a second conductor that is galvanically isolatedfrom the first conductor. In the illustrated example, the secondconductor includes transmitter conductive loop 408 (which is one exampleof transmitter winding 108). As shown in the illustrated example, thetransmitter conductive loop 408 is disposed proximate to the receiverconductive loop 410 to provide a magnetically coupled communication linkbetween the transmitter conductive loop 408 and the receiver conductiveloop 410 in accordance with the teachings of the present invention. Inaddition, FIG. 4 also shows leads 472 and 474, die attach pad 476, anddie attach pad 478. The square numbered as 471 illustrates the profileof the lead frame 400 that is disposed within the encapsulated portionof the integrated circuit package. In other words, elements within theprofile 471 are disposed within the encapsulated portion of theintegrated circuit package. Further shown in FIG. 4 are a transmitter402, a receiver 406, pads 479, 480, 481, 482, and 488, and bond wires483, 484, 485, 486, and 490. FIG. 4 is one example of a magneticcoupling configuration of a transmitter winding, receiver winding, andcancellation winding as discussed with respect to the FIG. 1B.

It is appreciated that the lead frame 400 illustrated in FIG. 4 sharesmany similarities with the lead frame 300 illustrated in FIG. 3 with theaddition of pad 488 and bond wire 490. Further, the signals produced byreceiver conductive loop 410 and cancellation conductive loop 412 arereceived separately by receiver 406.

The portion of the lead frame 400 shaded by dots in FIG. 4 correspondsto the receiver conductive loop 410. Bond wire 490 is attached to theportion of the lead frame 400 corresponding to the receiver conductiveloop 410 utilizing known bonding techniques. Bond wire 490 couples toreceiver 406 through pad 488 to complete the receiver conductive loop410. In addition, the portion of the lead frame 400 shaded bycross-hatching in FIG. 4 corresponds to the cancellation conduction loop412. Bond wire 486 is attached to the portion of the lead frame 400corresponding to the cancellation conduction loop 412 utilizing knownbonding techniques. Further, the bond wire 486 couples to receiver 406through pad 482 to complete the cancellation conduction loop 412.Further, bond wire 485 is attached to die attach pad 478 using knownbonding techniques and is coupled to the receiver 406 through pad 479.In one example, bond wire 485 and pad 479 provide the coupling to groundfor both the receiver conductive loop 410 and the cancellationconductive loop 412. As shown in the example depicted in FIG. 4,beginning from a reference point such as for example pad 479, receiverconductive loop 410 is wound in a counter-clockwise direction whilecancellation conductive loop 412 is wound in an opposite or clockwisedirection relative to receiver conductive loop 410. In the illustratedexample, transmitter conductive loop 408 is wound in the clockwisedirection from a reference point such as pad 480 of transmitter 402. Ingeneral, the transmit signal is sent from the pad 480 in a clockwisedirection around transmitter conductive loop 408. In one example, thetransmitter conductive loop 408 substantially surrounds the receiverconductive loop 410. In one example, the transmitter conductive loop408, the receiver conductive loop 410, and the cancellation conductiveloop 412 are all encapsulated in insulating material within theencapsulated portion of the integrated circuit package and are alldisposed substantially in the same plane.

FIG. 5 illustrates another example lead frame 500 disposed substantiallywithin the encapsulated portion of an integrated circuit package inaccordance with the teachings of the present invention. In theillustrated example, lead frame 500 includes a first conductor includingreceiver conductive loop 510 (which is one example of receiver loop110). In one example, the lead frame 500 also includes a third conductorincluding the cancellation conductive loop 512 (which is one example ofcancellation winding 112). However, as will be discussed in furtherdetail below, in another example the first conductor may also includethe cancellation conductive loop 512. As shown in the illustratedexample, lead frame 500 also includes a second conductor that isgalvanically isolated from the first conductor. In the illustratedexample, the second conductor includes transmitter conductive loop 508(which is one example of transmitter winding 108). As shown in theillustrated example, the transmitter conductive loop 508 is disposedproximate to the receiver conductive loop 510 to provide a magneticallycoupled communication link between the transmitter conductive loop 508and the receiver conductive loop 510 in accordance with the teachings ofthe present invention. In addition, FIG. 5 also shows leads 572 and 574,die attach pad 576, and die attach pad 578. The square numbered as 571illustrates the profile of the lead frame 500 that is disposed withinthe encapsulated portion of the integrated circuit package. In otherwords, elements within the profile 571 are disposed within theencapsulated portion of the integrated circuit package. Further shown inFIG. 5 are a transmitter 502, a receiver 506, pads 579, 580, 581, 582,and 588, and bond wires 583, 584, 585, 586, 589, and 590. FIG. 5 isanother example of a magnetic coupling configuration of a transmitterwinding, receiver winding, and cancellation winding as discussed withrespect to the FIG. 1B.

It is appreciated that the lead frame 500 illustrated in FIG. 5 sharesmany similarities with the lead frame 400 illustrated in FIG. 4. Onedifference, however, is that the cancellation conductive loop 512 iscoupled to die attach pad 578 and receiver conductive loop 510 through aconnection through receiver 506. For instance, in one example, thecancellation conductive loop 512 is coupled to die attach pad 578through pad 579 and bond wires 585 and 589. FIG. 5 also shows theaddition of pad 588 and bond wire 590. Thus, both the receiverconductive loop 510 and cancellation conductive loop 512 are coupledtogether and are therefore included as part of the first conductor asthey are coupled together through receiver 506 in the depicted example.

The portion of the lead frame 500 shaded by dots in FIG. 5 correspondsto the receiver conductive loop 510. Bond wire 590 is attached to theportion of the lead frame corresponding to the receiver loop 510utilizing known bonding techniques. Bond wire 590 attaches to pad 588,which is coupled to receiver 506 to complete the receiver conductiveloop 510. Further, bond wire 585 is attached to die attach pad 578 usingknown bonding techniques and is coupled to the receiver 506 through pad579. In one example, bond wire 585 and pad 579 provide the coupling toground for both the receiver conductive loop 510 and the cancellationconductive loop 512.

In addition, the portion of the lead frame 500 shaded by cross-hatchingin FIG. 5 corresponds to the cancellation conductive loop 512. Bond wire586 is attached to the portion of the lead frame 500 corresponding tothe cancellation conductive loop 512 utilizing known bonding techniques.Further, the bond wire 586 attaches to pad 582, which is coupled toreceiver 506 to complete the cancellation conductive loop 512. Bond wire589 attaches to the cancellation conductive loop utilizing knowntechniques and is coupled to receiver 506 through pad 579. As shown inthe example depicted in FIG. 5, beginning from a reference point such asfor example pad 579, receiver conductive loop 510 is wound in acounter-clockwise direction while cancellation conductive loop 512 iswound in an opposite or clockwise direction relative to receiverconductive loop 510. In the illustrated example, transmitter conductiveloop 508 is wound in the clockwise direction from a reference point suchas pad 580 of transmitter 502. In general, the transmit signal is sentfrom the pad 580 in a clockwise direction around transmitter conductiveloop 508. In one example, the transmitter conductive loop 508substantially surrounds the receiver conductive loop 510. In oneexample, the transmitter conductive loop 508, the receiver conductiveloop 510, and the cancellation conductive loop 512 are all encapsulatedin insulating material within the encapsulated portion of the integratedcircuit package and are all disposed substantially in the same plane.

FIG. 6 illustrates an example integrated circuit package 600, inaccordance with teachings of the present invention. The outline 671represents the encapsulated portion of integrated circuit package 600and is analogous to the profiles 371, 471, and 571 shown in FIGS. 3, 4and 5. The outline 671 denotes the profile and encapsulated portion ofintegrated circuit package 600. Terminals 692 and 694 couple to leadsinternal to the integrated circuit package 600, such as leads 372 and374, leads 472 and 474, or leads 572 and 574 shown above in FIGS. 3, 4,and 5. Circuits external to the integrated circuit package 600 may thenbe coupled to terminals 692 and 694.

For purposes of this disclosure, an “encapsulation” of an integratedcircuit package may be considered to be any external body, encasing ormolding that surrounds or encloses a portion of the lead frame which mayinclude one or more integrated circuit dice disposed therein, as well asconnections from the integrated circuit die pads to the lead frame andpins of the integrated circuit package. An example encapsulation may bemade from molded plastic, ceramic caps or the like. In some examples,the encapsulation of the integrated circuit package may or may notprovide hermetic sealing to protect the items encased therein fromexternal elements.

Those that are skilled in the art would appreciate that the galvanicisolation provided by communication link built according to teachings ofthis invention need not necessarily be preserved at the system level tobenefit from the teachings of this invention. For example, thecommunication link may be used to communicate between two parts of anon-isolated power converter system such a buck converter, half bridgeconverter and the like, that are referenced to different voltages orthat have changing voltage levels between them.

The above description of illustrated examples of the present invention,including what is described in the Abstract, are not intended to beexhaustive or to be limitation to the precise forms disclosed. Whilespecific embodiments of, and examples for, the invention are describedherein for illustrative purposes, various equivalent modifications arepossible without departing from the broader spirit and scope of thepresent invention. Indeed, it is appreciated that the specific examplevoltages, currents, frequencies, power range values, times, etc., areprovided for explanation purposes and that other values may also beemployed in other embodiments and examples in accordance with theteachings of the present invention.

What is claimed is:
 1. An integrated circuit package, comprising: an encapsulation; a lead frame, a portion of the lead frame disposed within the encapsulation, the lead frame comprising: a first conductive loop having a first end and a second end, wherein a first voltage is induced between the first and second ends of the first conductive loop in response to an external magnetic field that passes through the integrated circuit package; and a second conductive loop having a third end and a fourth end, wherein a second voltage is induced between the third and fourth ends in response to the external magnetic field that passes through the integrated circuit package, wherein the first conductive loop is coupled to the second conductive loop such that the first voltage between the first and second ends is substantially canceled by the second voltage between the third and fourth ends.
 2. The integrated circuit package of claim 1 wherein a direction along which the external magnetic field passes through a plane of the first conductive loop is substantially the same as a direction along which the external magnetic field passes through a plane of the second conductive loop.
 3. The integrated circuit package of claim 2 wherein the plane of the first conductive loop is substantially the same as the plane of the second conductive loop.
 4. The integrated circuit package of claim 1 wherein the second end of the first conductive loop is coupled to the fourth end of the second conductive loop, wherein a combined voltage induced in response to the external magnetic field between the first end and the third end is substantially zero.
 5. The integrated circuit package of claim 1, wherein the first conductive loop and the second conductive loop are coupled to a receiver circuit.
 6. The integrated circuit package of claim 1 wherein a direction along which a signal magnetic field passes through a plane of the first conductive loop is substantially opposite to a direction along which the signal magnetic field passes through a plane of the second conductive loop.
 7. The integrated circuit package of claim 6 wherein a third voltage is induced between the first and second ends of the first conductive loop in response to the signal magnetic field, and wherein a fourth voltage is induced between the third and fourth ends of the second conductor in response to the signal magnetic field.
 8. The integrated circuit package of claim 7 wherein the second end of the first conductive loop is coupled to the fourth end of the second conductive loop, wherein a combined voltage induced in response to the signal magnetic field between the first end and the third end is substantially equal to a sum of the third and fourth voltages.
 9. The integrated circuit package of claim 1, wherein the first conductive loop is coupled out of phase with the second conductive loop.
 10. The integrated circuit package of claim 1 further comprising an arithmetic operator circuit coupled to the first and second ends of the first conductive loop to receive the first voltage, and coupled to the third and fourth ends of the second conductive loop to receive the second voltage, wherein the arithmetic operator circuit is coupled to perform an arithmetic operation on the first and second voltages.
 11. The integrated circuit package of claim 10 wherein the arithmetic operator circuit is coupled to perform a subtraction operation on the first and second voltages.
 12. The integrated circuit package of claim 1 further comprising a third conductive loop disposed within the encapsulation proximate to the first conductive loop to provide a communication link between the first and third conductive loops.
 13. The integrated circuit package of claim 12 further comprising a transmitter circuit coupled to the third conductive loop.
 14. The integrated circuit package of claim 1 wherein the first conductive loop and the second conductive loop are substantially the same size. 